The present invention relates to a method of ensuring the sterility of distillate in a multi-stage distilling machine.
The present invention also relates to a device for ensuring the sterility of distillate in a multi-stage distilling machine which comprises numerous columns operating at different operating temperatures. The operating temperatures are stepwise, i.e., incremental. The distilling machine also includes a flow line for feed water and a supply line for steam.
A multi-stage distilling machine typically comprises several columns, usually four, five or six columns. With respect to the prior art, reference is made to Finnish Patent No. 47,083, corresponding to U.S. Pat. No. 3,875,017, which describes a multi-stage distilling machine. A stepwise lower distillation temperature prevails in the different columns of the distilling machine of this patent, for instance, so that the operating temperature in the first column is about 143.degree. C., in the third column about 125.degree. C., in the fourth column about 120.degree. C., in the fifth column about 110.degree. C. and in the sixth or the last column about 100.degree. C. Thus, there is a stepwise decrease from the first column to the last column.
The U.S. standard GMP (Good Manufacturing Practice) defines the minimum action time (F.sub.o) as about 8 minutes for moist-heat sterilization at a temperature of about 121.degree. C. Since the Z-value in moist-heat sterilization is about 10.degree. C., F.sub.o would be about 0.8 minutes at a temperature of about 131.degree. C. and, in a corresponding manner, 0.08 minutes at a temperature of about 141.degree. C. The above-mentioned numerical values indicate that the water to be distilled must be maintained at these temperatures for the minimum times in order to be certain that the distillate is definitely sterile.
In the first and the second columns in a multi-stage distilling apparatus, distillation generally takes place at temperatures and during certain times of action that ensure the sterility of distillate. In the last or penultimate columns, in which the operating temperature is only about 100.degree. C. or about 105.degree. C., there is no certain guarantee of the fact that the distillate would be sterile.